This invention pertains to an integrated process for hydro-oxidizing an olefin with oxygen in the presence of hydrogen to form an effluent stream comprising an olefin oxide, water, unconverted olefin, oxygen, and hydrogen and subsequently separating the effluent stream to obtain therefrom an olefin oxide product.
Olefin oxides, such as propylene oxide, are used to alkoxylate alcohols to form polyether polyols, which find wide-spread utility in the manufacture of polyurethanes and synthetic elastomers. Olefin oxides are also important intermediates in the manufacture of alkylene glycols, such as propylene glycol, and alkanolamines, such as isopropanolamine, which are useful as solvents and surfactants.
In past years several patents have disclosed gas and liquid phase processes for the direct hydro-oxidation of olefins having three or more carbon atoms (C3+) with oxygen in the presence of hydrogen to form corresponding olefin oxides. Catalysts for such processes are disclosed to comprise gold, silver, noble metals, such as palladium and platinum, or mixtures thereof, and optionally one or more promoters, such as alkali, alkaline earth, and rare earth elements, deposited on a titanium-containing support, such as, titania or a porous titanosilicate. Representative patents disclosing such hydro-oxidation processes include the following: EP-A1-0709360, WO 98/00413, WO 98/00414, WO 98/00415, U.S. Pat. No. 6,255,499, WO 03/062196, WO 96/02323, WO 97/25143, and WO 97/47386.
In gas phase hydro-oxidation processes, a gaseous effluent stream obtained from a hydro-oxidation reactor and comprising olefin oxide, water, and unconverted olefin, oxygen, and hydrogen is typically fed to a quench tower or column containing a liquid absorbent or solid adsorbent, wherein the olefin oxide is selectively removed from the effluent stream. Representative art disclosing the aforementioned separation methods include U.S. Pat. No. 4,990,632, U.S. Pat. No. 5,532,384, and US 2003/0031624 A1.
If a liquid absorbent is employed, the resulting liquid stream containing the olefin oxide dissolved in the absorbent is typically fed to a stripper column to recover a crude olefin oxide product. In this method, typically, a large quantity of absorbent is required; the olefin oxide is considerably diluted; and as a consequence, the absorbent and stripper columns are generally designed to handle a large quantity of liquid. Also, the stripper column may require a large energy input to meet the energy requirements for separating the olefin oxide from the absorbent. An unacceptably large temperature cycle may result between the absorbent column and the stripper column, between heating the olefin oxide-absorbent mixture in the stripper column and subsequently cooling the absorbent for recycle to the absorbent column. Moreover, the stripper column usually separates a crude olefin oxide product from the bulk absorbent, thereby necessitating a third distillation for recovery of a purified olefin oxide.
If the solid adsorbent method is employed, the process is cyclic rather than continuous, because the adsorbed olefin oxide must be desorbed from the column in a separate step. Moreover, at some point the adsorbent becomes saturated with the olefin oxide and needs to be regenerated. The solid adsorbent method can be facilitated by the use of two or more adsorbent columns operated in alternating cycles of adsorption and desorption; but such a multi-column method increases capital investment and operating costs.
Neither the liquid absorbent nor solid adsorbent method is completely satisfactory for commercialization. In view of the above, the art would benefit from integrating the gas phase hydro-oxidation process with an improved product separation method. Beneficially, such a process should operate continuously rather than intermittently; should avoid unacceptable dilution of the olefin oxide product; should lower energy demands and reduce temperature cycling; and should reduce to the extent possible capital investment and operating costs.